Which oil is the best synthetic motor oil?

by Search for Parts – Updated March 1st, 2020

Most consumers know synthetic oil lasts longer and performs better than traditional oil. What they don’t realize is that not all synthetics are created equal. While traditional oils are petroleum-based, synthetics can be made from several different base stocks, such as hydro-waxes, polyalphaolefin, diesters, and polyolesters, it’s these ingredients that define a synthetic oil and differentiate one brand from another. In 2013, Amsoil conducted an analysis to see how its unique 5W-30 synthetic formula stacks up against the competition. The procedure was carried out in a laboratory in accordance with the American Society of Testing and Materials (ASTM). 

Testing to determine synthetic oil quality 
To ensure a level playing field, all oils tested were 5W-30 weight and recommended by the American Petroleum Institute (API). The products included were AMSOIL Signature Series Synthetic Motor Oil, Castrol Edge with Titanium Fluid Strength Technology, Lucas Synthetic, Mobil 1 Extended Performance, Pennzoil Ultra, Petro-Canada SUPREME Synthetic, Quaker State Ultimate Durability, Red Line High Performance Motor Oil, Royal Purple High Performance Motor Oil, and Valvoline SynPower Full Synthetic Motor Oil.

Each oil went through five tests: four-ball wear, total base number, cold cranking viscosity, thermo-oxidation engine oil simulation, and NOACK volatility. The overall annual cost of each was also calculated. 

Four-ball wear test
The four-ball wear test indicates how well a lubricant can shield metal components from one another inside an engine. During the procedure, metal balls are cover in oil, then vibrated in a test machine. After the process is complete, the balls are inspected for “scarring” to determine how well the lubricant protected them from one another. The smaller the scar, the better the performance. During the test, the top four oils had scars under 0.40 mm. AMSOIL came in at approximately 0.35 mm, making it the winner. 

Best synthetic oils 4 ball wear test

Total base number
An oil’s ability to control acids is indicated by its Total Base Number (TBN). The TBN can also be used to determine how fast a lubricant will degrade during service. A high rating signifies a greater ability to defend against corrosion.  AMSOIL tested two numbers higher than the other oils, making it the winner in this category. 

total base number test of synthetic oils

Cold cranking viscosity test 
In frigid temperatures, engine oil tends to thicken, leading to difficult starting. A cold cranking test was performed to see how the lubricants would perform in a -22º F climate. In sub-zero temperatures, AMSOIL had the lowest viscosity of all the oils, indicating it would provide the easiest engine starting. 

cold crank viscosity test of synthetic oils

Thermo-oxidation engine oil simulation
Under extreme heat, engine oil loses its effectiveness, allowing harmful deposits to accumulate. A thermo-oxidation engine oil simulation is used to determine the amount of sediment formed when a lubricant gets extremely hot. During this test, only Castrol and AMSOIL came in with 5 mg of deposits or less. Castrol had approximately 3.5 mg, making it the winner, whereas AMSOIL had 5 mg. 

best synthetic motor oil brands testing

NOACK volatility test
The NOACK volatility test determines how well a lubricant will retain its weight under extreme temperatures. This is determined by measuring weight of the oil before and after testing. In this situation, Red Line High Performance Motor Oil performed the best with approximately 5.5% weight loss. AMSOIL, however, also did well, losing only about 7% of its weight. 

noack test of the best synthetic motor oils

Overall test results  
AMSOIL is proof that not all synthetic oils are created equal. In four out of six categories, the industry-leading product scored the highest. It also performed the best overall, consistently ranking among the top three products. All tests were perfomed by an independent third party which contributes to the validity of these tests. See source below.


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